Mounting of gauged load bearing members

ABSTRACT

This invention is drawn to an apparatus for lifting and weighing a container, including a pair of fork tines engagable with said container and mounted on a supporting structure, each fork tine having a vertically disposed web provided with transducers responsive to strain therein to determinate the weight imposed on the tines by the container, characterized in that each tine is attached to the supporting structure by the bolts passing through said web and through a vertical flange located on only one side of said web and attached to the supporting structure.

FIELD OF THE INVENTION

In International patent application No. WO 94/03784 there are describedtechniques for the measurement of loads by means of strain gaugeslocated on structures which are not otherwise adapted for loadmeasurement, in which the influence of secondary force on themeasurement of the load is compensated by the measurement secondarystrain in the structure.

The present invention is directed to improving the performance of suchan arrangement in the case of weighing garbage by means of suchcompensated strain measurement applied to the forks of a garbage skiplifting and transporting vehicle.

BACKGROUND ART

Before the introduction of the approach to weighing which is disclosedin the above-mentioned application, attempts to measure loads in suchadverse situations as garbage handling equipment or other hostileweighing environments had followed the conventional wisdom of load celltechnology, and devices have been constructed using parallelogramlinkages and other complex means of isolating a load cell or cells fromspurious strains. None of these approaches has succeeded in achievingsufficiently accurate and repeatable results, with durability.

The methods described in the above-mentioned International applicationinvolve a radical approach to the problem of dealing with variations instrain field orientation. In these methods, the primary sensing axis ofa principal strain gauge is orientated for response to variation in aprincipal force, and the effect of secondary forces or secondary strainon the principal gauge is corrected by means of a secondary strain gaugelocated and orientated so that its response represents the influence ofthe secondary forces on the response of the principal gauge.

As disclosed in the above application, garbage may be weighed in thisway by the application of strain gauges, to the tines of forks employedfor the transport of garbage skips. The forks are mounted at theirproximal ends on a supporting structure, and a gauging region isprovided near the supported end of each fork. In this region a principalstrain gauge is formed by a pair of strain gauge elements, one on eachside of the flange of the fork, provided with their sensing gridsorientated to respond to shear strain and thereby to provide anindication of the load on the fork.

A secondary gauge comprising a second pair of strain gauge elements isalso provided, adjacent to the primary gauge, the grids of the secondarygauge being orientated to respond to bending strain and compression ortension strain. The first and second pairs of gauges are connected inrespective Wheatstone bridges, and these bridges are interconnected withopposite polarity so that the output of the second gauges opposes thatof the first, and the relative influence of the second gauges isadjusted to obtain the required compensation.

SUMMARY OF THE INVENTION

We have found that even with the compensation afforded by the use of theinvention disclosed in the above-mentioned application, weight readingsobtained by using that method in the case of such garbage truck forksmay suffer from a lack of desirable linearity and repeatability.

Investigations of the sources of such repeatability problems have leadus to the discovery that this is due to the methods of mounting of thefork tines which have been used in the prior art. We have found that ifthe variable orientation of the strain field arising from distortioncaused by reaction forces at the mounting end of the fork is stabilised,greatly improved load measurement results are obtained. We havetherefore hypothesised that conventional methods of fork mounting, andindeed others which have been adopted as apparently better suited wherethe forks are to be gauged, have contributed to a lack of repeatabilityand linearity by introducing shifting strain patterns into the fork fromthe lifting mechanism.

What we have suprisingly found is that significantly superior results,in terms of the repeatability and linearity of the measurementsobtained, are found if the tines are mounted by what is referred toherein as single- sided through bolting, onto a flange fixed to orforming part of the supporting structure. By single-sided throughbolting we mean the case where bolts are passed horizontally through theweb of the tine and a single flange, the web being thus mounted on thisflange solely by such bolting.

The invention therefore resides in apparatus for the lifting andweighing of a container, including a pair of fork tines engagable withsaid container and mounted on a supporting structure, each fork tinehaving a vertically disposed web provided with transducers responsive tostrain therein to enable the determination of the weight imposed by thecontainer on the tines, characterised in that each tine is attached tothe supporting structure by bolts passing through said web and through avertical flange located on only one side of said web and attached to thesupporting structure.

In the case where the supporting structure is a cross bar, a flange maybe welded to the cross bar at the desired location of each tine. Where across bar mounting is not use, and instead, for example, the tines areto be mounted directly on side members of the lifting structure, thelatter will be modified to accommodate the side bolting method used.

The pattern of bolting is preferably such that two lines of bolts areemployed, one in each of two quadrants about the cross bar or mountingregion. These lines of bolts may be straight or curved, and the axes ofthe quadrants may be at any angle. In the simplest and preferred form,illustrated herein, a line of bolts is provided respectively above andbelow the cross bar.

By way of example only the following description deals with severalembodiments of the invention illustrated in the drawings. No generaldescription of the weighing system and the transport vehicle with whichit intended to be used is given here, as it will be quite familiar tothose in the relevant art.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates in fragmentary side elevation a tine attached bymeans of opposed flanges;

FIG. 2 illustrates in fragmentary side elevation a single sided throughbolting method according to a first embodiment of the invention;

FIG. 3 is a side elevation of a removable mounting device providing forsingle sided through bolting a according to the invention;

FIG. 4 is an end elevation of the device of FIG. 3 mounted on a crossbar; and

FIG. 5 is a fragmentary side elevation of an alternative embodiment ofthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an arrangement which, although being a straightforwardtechnical solution, we have found to be unsatisfactory. Here each forktine 10 carries a flange 13 to which it is welded, and this flange isbolted to a similar flange 14 welded to the cross-bar 11. We have foundthat non-repeatable and non-linear results are obtained, and this isbelieved to be due to the fact that distortion of the cross-bar willoccur readily and strain field variations in the plane of the fork 10arising from distortion of the cross-bar 11 are readily able to enterthe fork. Since furthermore such distortion will vary with variations ofbending moment due to variation of the load line of the applied force onthe fork, or due to the action of extraneous forces on the fork, thesestrain field variations will produce non-linear and non-repeatablemeasurements of the load.

Configurations of mounting arrangements in accordance with the inventionare shown in FIGS. 2, 3 and 4.

In the FIG. 2 embodiment, for direct fixing to the cross-bar, a flange18 is welded continuously at 20 on all four sides to the cross-bar 11,and the end of the tine, is through-bolted at 21 to the flange at thetop and the bottom. Stiffening flanges 22 are provided on the end regionof the tine.

Strain gauges are provided on the web at 25 as described above.

In the embodiment shown in FIGS. 3 and 4, a structure similar to that ofFIG. 2 is shown, in this case for a removable mounting. Slidable on thecross-bar 11 is a box member 23 to which is continuously welded a flange18. The tine 10 is through-bolted to the flange 18 in the same manner asshown in FIG. 2. Additional stiffening flanges 24 may also be providedfurther to reduce distortion of the box 23.

The lifting mechanisms typically employed on garbage trucks are built aslightly as possible while still being able to lift the required load,and therefore distort considerably with load variations. The flange 18should therefore be heavy enough so that its inherent stiffnesssubstantially isolates the tine from the distortions which occur in thelifting mechanisms with variations in the load on the fork.

The performance of the arrangements shown in FIGS. 2, 3 and 4 representsa dramatic improvement. It has even been found that load measurementsand no-load return readings are unaffected by slackening off themounting bolts from their recommended torque of 250 lbft to 110 lbft.

Shown in broken lines at 24 in FIG. 3 are other possible locations forbolts mounting the tine to the flange 18. With a suitably shaped end forthe tine, bolting could be carried out in any of these regions, but ithas been found that best results are achieved if lines of bolts areemployed in at least two of the quadrants seen in FIG. 3.

In the FIGS. 3 and 4 embodiments, stiffening members in the plane of thetine are used to minimize distortion before it reaches the tine. In analternative approach, stiffening is achieved in the mounting end of thetine itself, by increasing the height and/or the thickness of the forkbetween the mounting and the strain gauges so that the base of the tineacts as a stiffening flange.

FIG. 5 illustrates an alternative approach to the bolt layout, in whichthe two lines of bolts 26 are vertical and both located on the side ofthe flange 18 which faces the tine, that is to say the portion of theflange extending toward the tine.

What is claimed is:
 1. Apparatus for the lifting and weighing of a container, including a pair of fork tines engagable with said container and mounted on a supporting structure, each fork tine having a vertically disposed web provided with transducers responsive to strain therein to enable the determination of the weight imposed by the container on the tines, characterised in that each tine is attached to the supporting structure by bolts passing through said web and through a vertical flange located on only one side of said web and attached to the supporting structure.
 2. Apparatus according to claim 1 wherein said bolts are provided in at least two of four quadrants when viewed in the direction of the bolt axes.
 3. Apparatus according to claim 2, wherein said supporting structure is a crossbar, said locations being disposed about said crossbar.
 4. Apparatus according to claim 3 wherein each tine web is provided with a relieved portion for the reception of the crossbar.
 5. Apparatus according to claim 4, said locations being a line of bolts located above the crossbar, a line of bolts located below the crossbar, a line of bolts located on the side of the crossbar from which the tine extends, and a line of bolts located at the side of the crossbar opposite the side from which the tine extends.
 6. Apparatus according to claim 1 wherein said bolts are provided in two vertical rows in the portion of said web which extends toward said tine.
 7. Apparatus for lifting and weighing of a container, including a pair of fork tines engagable with said container and mounted on a supporting structure, each fork tine having a vertically disposed web provided with transducers responsive to strain therein to enable the determination of the weight imposed by the container on the tines, characterized in that each tine is attached to the supporting structure by bolting said web to a vertical flange located on only one side of said web and attached to the supporting structure. 